This application claims under 35 U.S.C. xc2xa7119(a)-(d) or xc2xa7365(b) of Germany Application No. 20106262.3 filed Apr. 10, 2001.
The invention relates to a blast nozzle, especially for drying contact lenses.
Contact lenses, which are to be manufactured economically in large unit numbers, are preferably manufactured by the so-called mould or full-mould process. In these processes, the lenses are manufactured into their final shape between two mould halves, so that there is no need to subsequently finish the surfaces of the lenses, nor to finish the edges. Mould processes are described for example in PCT patent application WO 87/04390 or in EP-A 0 367 513.
In these known mould processes, the geometry of the contact lens to be manufactured is defined by the mould cavity. The edge of the contact lens is likewise formed by the mould which normally consists of two mould halves. The geometry of the edge is defined by the contour of the two mould halves in the area in which they make contact. The contact lenses produced in this manner are moulded parts having little mechanical stability and a water content of more than 60% by weight. After manufacture, the lens is checked using measuring techniques, then packaged and subjected to heat sterilisation at 121xc2x0 C. in an autoclave.
To manufacture a contact lens, first of all a certain amount of the flowable starting material is placed in the female mould half. Afterwards, the mould is closed by placing the male mould half thereon. Normally, a surplus of starting material is used, so that, when the mould is closed, the excess is expelled into an overflow area adjacent to the outer mould cavity. The subsequent polymerisation or crosslinking of the starting material takes place by radiation with UV light, or by heat action, or by another non-thermal method.
Subsequently, the contact lenses thus produced must be removed from the mould halves, preferably from the female mould halves. To do this, a gripper is provided for example, which is moved in the direction of the mould half and removes the lenses from the mould half by applying suction to the lenses with a vacuum. After removing the lenses, the gripper arm moves into another position, so that further procedures can be carried out, such as drying of the contact lenses on the gripper, checking of the contact lens using an image-processing system, placing the contact lenses in a package, and rinsing and drying of the gripper itself. To this end, the gripper may be, for example, star-shaped, and in this configuration represents the connecting link between manufacturing the contact lenses and primary packaging. Only the lenses that are centred by the gripper and grasped smoothly can be checked by the image-processing system and subsequently deposited in the package. In addition to perfect removal of the lenses by the gripper, another essential prerequisite to attaining a high yield of the equipment is satisfactory presentation of the lens for the image processing process.
Usually prior to removal from the mould half, the contact lenses are first of all loosened and, if desired, also transferred from the male to the female mould half, since the actual removal of the contact lenses is preferably effected from the female mould half. To enable the apparatus to be operated most economically, several mould halves, preferably a figure of 10, can be held in one tool and grasped together by one gripper arm, which accordingly has 10 grippers.
An essential condition for providing good presentation of the contact lens for image processing is a lens that is as dry as possible, especially in the periphery. In a lens, defects such as bubbles and tears may occur as a result of the production process. However, if for example some drops are found on the lens due to the loosening procedure, the image processing system cannot distinguish between these artefacts and the actual defects, so that lenses which have no defects are also sorted as defective lenses. Therefore, the lenses on the gripper have to be dried by a drying nozzle. To dry the lenses, previously a nozzle of a concave shape was used. The shape was adapted to the design of the contact lens. Of course, during the drying process, interruptions always occurred. These were caused by lenses or lens residues falling from the gripper and by residues of the unpolymerised lens material.
The invention is concerned with the problem of ensuring optimum drying of the contact lenses on the gripper, whilst at the same time minimising interruptions in operations.
The invention solves this problem with the features indicated in claim 1. As far as further essential refinements are concerned, reference is made to the dependent claims.
Owing to the convex shape of the outer contour of the blast nozzle, defects on the edge of the lens in particular can be readily detected, since the drying process operates in optimum manner compared with a concave shape. In addition, a convex shape enables lenses or lens residues that drop down to slide along the nozzle and not to clog the nozzle jets any more.